[HIP] Remove hip/hc.amdgcn.bc from HIP Toolchains

Summary:
The hc.amdgcn.bc and hip.amdgcn.bc are removed in VDI build and no longer needed.

Reviewers: yaxunl

Reviewed By: yaxunl

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D48455

llvm-svn: 335634